Process for preshrinking highly oriented, low-pressure polyolefine filaments with chemical shrinking agents



PROCESS FOR PRESHRINKING HIGHLY ORI- ENTED, LOW-PRESSURE POLYQLEFHNE FILAMENIS WITH CHEMICAL SHRINKING AGENTS Wolfgang Jurgeleit, Davenport, Iowa, assignor to Vereinigte Glanzstoif-Fabriken, A.G., Wuppertal-Elberfeld, Germany No Drawing. Filed Apr. 10, 1958, Ser. No. 727,540 Claims priority, application Germany Apr. 17, 1957 13 Claims. (Cl. 8130.1)

This invention relates to an improved process for preshrinking a highly-oriented, low-pressure polyolefine filamentary material, especially polyethylene monofilaments, threads, yarns, and the like, either before or after incorporation in a textile product such as a fabric or similar woven or felted material. In particular, the invention is concerned with an improved process or method of preshrinking low-pressure polyolefine filaments wherein the residual capacity for further shrinkage is reduced to an absolute minimum for all practical purposes.

The extent to which artificial filaments tend to shrink is dependent upon their chemical composition and molecular structure and will be influenced to a large degree by the tensions and physical changes imparted to the filament as it is extruded and stretched in the spinning process. In general, filaments of high molecular weight synthetic polymers, especially the highly-oriented, lowpressure polyolefine polymers, whether stretched hot or cold, have an exceptionally high capacity for shrinkage. Thus, low-pressure polyethylene filaments will shrink from about 4 to 7% when treated for one hour in boiling water, depending upon the particular conditions employed in spinning the filament from the polymer. For this reason, it has been necessary to preshrink polyolefine filaments, either as such or in the form of a textile fabric, in order to provide a dimensionally stable product. Although the highly-oriented, low-pressure polyolefine filaments and fabrics have many desirable properties, their high shrinkage capacity prevents their use in many applications where exposure to heat, e.g., merely washing in hot water, causes even a slight shrinkage of 1 or 2%.

Various methods have been devised for preshrinking both high-pressure and low-pressure polyolefine filamentary materials, and in most instances, an attempt is made merely to control the degree of shrinkage such that the material will still retain a residual capacity for further shrinkage. In order to obtain filaments which have been completely preshrunk for practical purposes, they must.

usually be treated in boiling water or with steam for about one hour, a shorter period of time being effective only to partially reduce the shrinkage capacity of the filament or fabric. The length of time required for complete preshrinking is about 10 to 20 minutes if a hot salt solution is employed. The same effect can also be btained by using hot glycol or glycerine baths but a temperature of more than 120 C. is required, and although complete preshrinking is possible, the treatment time is at least 10 minutes and preferably at least 20 minutes or more.

The results which can be achieved with prior processes are satisfactory with respect to a complete preshrinking, i.e., to provide dimensional stability when the filamentary material is subjected to an after-treatment for one hour in boiling water. However, it is necessary to employ relatively long periods of treatment which preclude continuous operation, unless very large baths are used with a correspondingly high heat requirement, in which case 2,973,242 Patented Feb. 28, 1961 the procedure becomes uneconomical. If higher temperatures are employed, particularly above C., in an attempt to reduce the time required for the preshrinking treatment, the relatively low-melting polyolefine filaments may become irreparably damaged or deformed.

One object of the present invention is to provide an improved process for preshrinking polyolefine filaments which can be accomplished in a very short period of time, whereby the process may be carried out continu-v ously and at the same time provide a product which is substantially stable or non-shrinking when subsequently treated for one hour with boiling water.

Another object of the invention is to provide a method of preshrinking polyolefine filaments at lower temperatures in order to avoid any possible damage to the filaments.

Still another object of the invention is to provide preshrunk polyolefine, particularly polyethylene, filaments having improved elasticity. I

Yet another object of the invention is to provide an improved continuous preshrinking of polyolefine filaments which can be carried out at a relatively low cost and with a minimum space requirement, thereby providing an efficient and economical process for commercial practice. This object includes a lower energy expenditure for maintaining the temperature of the treating bath as well as the avoidance of large baths and large quantities of material being treated at any one time.

In accordance with the invention, it has now been found that a highly-oriented, low-pressure polyolefine filamentary material can be substantially completely preshrunk, i.e., so as to reduce the shrinkage capacity of the filamentary material to zero as measured by subsequent boiling in water for one hour, by the improved method which includes immersing the filamentary material at a temperature of about 60 C. up to 90 C. in a normally liquid monoor bi-cyclic hydrocarbon having from 7 to 15, preferably 8 to 12, carbon atoms and characterized by a boiling point within the range of at least C. to about 290 C. and for a period of time of from about 5 seconds to 5 minutes. For continuous operation, the immersion or treatment about 10 to 60 seconds.

The so-called low-pressure polyolefines which are preshrunk by the process of the invention include only those lower aliphatic polyolefines which have become well-known as having useful fiber properties. Polyethylene filaments are especially useful in textile products, and therefore the invention is hereinafter described with particular reference to this material. Nevertheless, the preshrinking treatment of the invention is likewise applicable to polypropylene, polybutylene and polypentene filaments. Accordingly, it will be understood by those skilled in the art that the term polyolefines as employed herein is intended to include only those polymers of aliphatic monoolefines having 2 to 5 carbon atoms.

These low-pressure polyolefines are characterized by a high degree of orientationin their molecular configuration and have a high molecular weight, e.g., 70,000 and above, by comparison to the high-pressure polyolefines. The term low-pressure has been applied to these polymers in order to dilferentiate them from the high-pressure polymers, although the difference in physical properties is primarily due to the use of particular heterogeneous catalysts in the manufacture of low-pressure polyolefines. The particular catalysts required are well-known in the art and include, for example, metal alkyls or metal hydrides, such as aluminum alkyl, in combination with the heavy metal salts of the 4th to 8th groups of the periodic system. Chromium oxide precipitated upon argillaceous earth is also a very useful catalyst in the lowpressure process. Especially useful low-pressure polytime is preferably olefine filaments can be obtained by spinning the polymer in the manner set forth in my copending application, S.N. 664,289, filed June 7, 1957.

The highlyoriented, low-pressure polyolefines, and especially polyethylene, can be spun and then stretched either hot or cold to provide filaments which have excellent properties of tensile strength, elasticity, melting point, and stability against chemical attack. However, the stretched filament, even if heat-set (without shrinkage), has a shrinkage capacity of about 4 to 7%, and while various preshrinking treatments have been suggested for the purpose of partially reducing the shrinkage capacity of the filaments, it has been a particularly dilficult problem to economically produce a product which will resist further shrinkage when boiled for one hour in water.

The rapid and economical preshrinking of polyolefine filaments has been accomplished in accordance with the invention by treatment in a liquid bath which must consist essentially of a monoor bicyclic hydrocarbon having from 7 to 15, preferably 8 to 12, carbon atoms and having a boiling point within the range of at least 110 C. to about 290 C. These hydrocarbons must not contain substituents other than lower alkyl groups and therefore consist solely of carbon and hydrogen atoms.

Xylene is the most effective hydrocarbon for the practice of the invention, since it provides a rapid shrinking at a low temperature and is readily available and comparatively inexpensive. For example, the preshrinking of polyethylene filaments can be carried out by immersion in xylene at about 70 C, to 80 C. for a period of about 20 to 30 seconds, and these conditions represent the preferred method of the invention. Xylene is often employed as a solvent for polyethylene or other polyolefine polymers, and it was quite surprising therefore to find that it serves so well as a preshrinking bath. Rather than having any deleterious effect upon fiber properties, it provides an improved elasticity in the filaments as compared to those preshrunk filaments obtained in prior processes.

Other normally liquid aromatic, cycloaliphatic and mixed cycloaliphatic-aromatic hydrocarbons which are suitable as preshrinking baths, either alone or in admixture, e.g., with xylene, include the following: toluene, ethyl toluene, mesitylene, hemimellitine, pseudodocumene, butyl benzene, amyl benzene, cymene, curnene, pseudocumene prehnitol, isodurene, sym-triethyl benzene, unsymtriethyl benzene, tetraethyl benzene, alpha-methyl naphthalene, 1.6-dimethyl naphthalene, 1.2-dimethyl naphthalene, ethyl naphthalene, cyclooctane, cyclononane, indene, decalin, tetralin, methyl tetralin and ethyl tetralin. The preferred hydrocarbons are those having from 8 to 12 carbon atoms, and especially the aromatic hydrocarbons of the group consisting of xylene, cymene, ethyl toluene and ethyl naphthalene, and the hydrogenated atomatic hydrocarbons of the group consisting of decalin, tetralin and methyland ethyl-tetralin. Toluene is less effective than Xylene for rapid preshrinking, but because of its low cost and availability, it is also very useful if the time of treatment is extended or when it is admixed with other hydrocarbons in the liquid bath. Good results are obtained with the above-mentioned hydrocarbons provided that the bath temperature does not exceed 90 C. and the time of treatment is at least seconds, preferably about seconds or more up to about 5 minutes. Evaporation of the normally liquid hydrocarbon from the preshrinking bath must be avoided.

The advantages of the rapid preshrinking process carried out in accordance with the invention will become more apparent upon comparison with the customary method wherein boiling water is employed. Thus, a thread or tow of low-pressure polyethylene filaments, which has been made in the usual manner by extrusion and subsequent hot-stretching by about 800% and which has a shrinkage capacity of 6%, must be immersed in boiling water for at least about 30 minutes in order to reduce the shrinkage capacity to zero. 0n the other hand, the same effect can be achieved by the process of the invention it an -identical thread or tow is conducted through a xylene bath heated to about C. to C. for a period of contact of only about 20 to 30 seconds. If the temperature of the xylene is raised slightly, e.g., to 90 C. the contact period can be reduced even further. However, tempeartures above 90 C. must be avoided in all cases in order to avoid damaging the filaments.

In the process of manufacturing the filaments, the preshrinking treatment of the invention may follow immediately after the extruded threads have been stretched to the desired elongation and orientation. A continuous process is therefore possible by conducting a filament or group of filaments directly from a suitable stretching device at a uniform speed, preferably without tension, through the hot liquid hydrocarbon bath, and the resulting filaments can be readily washed free of excess hydrocarbon and dried, so as to provide preshrunk filaments suitable for further processing into a textile product which will be substantially shrink-resistant.

The invention is further illustrated by the following examples, but it will be understood that the invention is not limited to these examples.

Example 1 A yarn or tow of low-pressure polyethylene is manufactored by extruding or spinning the polyethylene into 30 individual filaments with an individual titer of 64 denier and has the following physical properties after hotstretching by 800%:

Tensile strength grams/denier 5.2 Elasticity percent 15 Shrinkage capacity do 7 (a) The yarn is immersed in boiling water for one hour causing the shrinkage capacity to fall to zero. The tensile strength of the yarn is reduced to 4.1 grams/ denier while the elasticity rises to 22%.

(b) An idetical yarn is conducted, immediately after stretching, through a xylene bath maintained at a tempuerature of 80 C. such that the yarn remains in contact with the bath for a period of 20 seconds. This treatment likewise reduces the shrinkage capacity of the yarn to zero. The tensile strength amounts to 4 grams/ denier while the elasticity has increased to 28%.

Example 2 A low-pressure polyethylene yarn, produced as in Example l and consisting of 30 individual filaments with an individual titer of 40 denier, has the following physical properties:

Tensile strength grams/denier 4.9 Elasticity "percent" 21 Shrinkage capacity do 7.2

The shrinkage capacity of this yarn is reduced to zero by conducting it through a bath of tetralin maintained at a temperature of C. The tensile strength is reduced to 4.5 grams/ denier while the elasticity is increased to 27%.

Example 3 one hour, and the elasticity is increased by a substantial amount.

In the foregoing specification and examples, the values given for shrinkage capacity represent the percent by which the filament length shortens upon subsequent treatmeat in boiling water for one hour. A shrinkage capacity of zero is required to provide a substantially shrink-resistant filamentary material for use in textile fabrics and the like which are subjected to normal climatic and washing temperatures of about 100 C. or less.

It will be noted in the examples that the tensile strength of the polyethylene yarn decreases While elasticity increases during the preshrinking. When the yarn is treated in accordance with the invention, the diminution of tensile strength corresponds approximately to that which is experienced with an hours treatment in boiling water. The elasticity, however, is substantially increased by the process of the invention as compared to the treatment in boiling water. Accordingly, the use of the normally liquid hydrocarbons of the invention is further advantageous in providing shrink-resistant fibers or filaments having an improved elasticity.

Although the process of the invention has been described with particular reference to preshrinking of monofilaments or bundles of filaments in the form of a yarn or thread, the preshrinking treatment is also applicable to finished fabrics or similar textile products with equally good results. Special effects, such as crenelated fabrics, are possible in fabrics which contain both polyethylene fibers and other types of natural or synthetic fibers which are not subject to the shrinking effect of xylene or other specific hydrocarbons which have been mentioned. The particular eifects obtained by this selective preshrinking of polyethylene filaments in a mixed fabric can also be achieved in fabrics consisting solely of polyolefine filaments Where two or more interwoven filaments having different shrinkage capacities are first made into the fabric prior to treatment in accordance with the invention.

The process of the invention is believed to provide for the first time a commercially successful and economical procedure for preshrinking polyolefine filaments, especially for continuous operation. In addition, the resulting shrink-resistant filaments or fabrics have improved properties of elasticity while retaining about the same tensile strength experienced in prior preshrinking methods. Furthermore, the preshrinking process of the invention is readily adapted to existing facilities and can be continuously operated with a minimum of supervision. The results obtained are uniform so as to provide a high quality shrink-resistant product.

The invention is hereby claimed as follows:

1. An improved process for preshrinking a highlyoriented, low-pressure polyolefine filamentary material selected from the group consisting of polyethylene, polypropylene, polybutylene and polypentene wherein the molecular weight of said polyolefine is at least about 70,000, which process comprises immersing said filamentary material free from tension at a temperature of about 60 C. up to 90 C. in at least one normally liquid hydrocarbon selected from the group consisting of xylene, toluene, ethyl toluene, mesitylene, hemimellitine, pseudodocumene, butyl benzene, amyl benzene, cymene, cumene, pseudocumene, prehnitol, isodurene, sym-triethyl benzene, unsym-triethyl benzene, tetraethyl benzene, alpha-methyl naphthalene, 1.6-dimethyl naphthalene, 1.2-dimethy1 naphthalene, ethyl naphthalene, cyclooctane, cyclononane, indene, decalin, tetralin, methyl tetralin and ethyl tetralin for a period of time of from about 5 seconds to 5 minutes and snfficient to reduce the shrinkage capacity of said filamentary material to zero as measured by subsequent boiling in water for one hour.

2. An improved process as claimed in claim 1 wherein said filamentary material is polyethylene.

3. An improved process as claimed in claim 2 wherein at least one of said normally liquid hydrocarbons is toluene.

4. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is xylene.

S. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is tetralin. 4

6. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is methyl tetralin.

7. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is ethyl tetralin.

8. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is decalin.

9. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is cymene.

10. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is ethyl toluene.

11. An improved process as claimed in claim 2 wherein said normally liquid hydrocarbon is ethyl naphthalene.

12. An improved process for continuously preshrinking a highly-oriented, low-pressure polyethylene filamentary material wherein the polyethylene has a molecular weight of at least about 70,000 which comprises immersing said filamentary material free from tension at a temperature of about C. up to 90 C. in a liquid hydrocarbon bath consisting essentially of xylene for a period of time of from 10 to 60 seconds sufficient to reduce the shrinkage capacity of said filamentary material to zero as measured by subequent boiling in water for one hour.

13. An improved process as claimed in claim 12 wherein the temperature of the xylene bath is maintained at about C. to C. and the period of immersion is about 20 to 30 seconds.

42, 1946, Pp. 10-12, 20-22 and 27. 

1. AN IMPROVED PROCESS FOR PRESHRINKING A HIGHLYORIENTED, LOW-PRESSURE POLYOLEFINE FILAMENTARY MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE, POLYPROPYLENE, POLYBUTYLENE AND POLYPENTENE WHEREIN THE MOLECULAR WEIGHT OF SAID POLYOLEFINE IS AT LEAST ABOUT 70,000, WHICH PROCESS COMPRISES IMMERSING SAID FILAMENTARY MATERIAL FREE FROM TENSION AT A TEMPERATURE OF ABOUT 60* C. UP TO 90* C. IN AT LEAST ONE NORMALLY LIQUID HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF XYLENE, TOLUENE, ETHYL TOLUENE, MESITYLENE, HEMIMELLITINE, PSEUDODOCUMENE, BUTYL BENZENE, AMYL BENZENE, CYMENE, CUMENE, PSEUDOCUMENE, PREHNITOL, ISODURENE, SYM-TRIETHYL BENZENE, UNSYM-TRIETHYL BENZENE, TETRAETHYL BENZENE, ALPHA-METHYL NAPHTHALENE, 1.6-DIMETHYL NAPHTHALENE, 1.2-DIMETHYL NAPHTHALENE, ETHYL NAPHTHALENE, CYCLOOCTANE, CYCLONONANE, INDENE, DECALIN, TETRALIN, METHYL TETRALIN AND ETHYL TETRALIN FOR A PERIOD OF TIME OF FROM ABOUT 5 SECONDS TO 5 MINUTES AND SUFFICIENT TO REDUCE THE SHRINKAGE CAPACITY OF SAID FILAMENTARY MATERIAL TO ZERO AS MEASURED BY SUBSEQUENT BOILING IN WATER FOR ONE HOUR. 